U.S. patent number 7,763,283 [Application Number 11/523,328] was granted by the patent office on 2010-07-27 for nitric oxide (no) releasing material.
This patent grant is currently assigned to Accord Biomaterials, Inc., The Regents of The University of Michigan. Invention is credited to Melissa M. Batchelor, Mark E. Meyerhoff, Bong Kyun Oh.
United States Patent |
7,763,283 |
Batchelor , et al. |
July 27, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Nitric oxide (NO) releasing material
Abstract
Biocompatible materials that have the ability to release nitric
oxide (NO) in situ at the surface-blood interface when in contact
with blood. The materials which may be polymers (e.g.,
polyurethane, poly(vinyl chloride), silicone rubbers), metals, such
as stainless steel, carbon, and the like are provided with
biocatalysts or biomimetic catalysts on their surface that have
nitrite, nitrate, and/or nitrosothiol-reducing capability.
Illustratively, the catalysts are adsorbed or immobilized at the
surface of the material. The catalysts can act on endogenous
nitrite, nitrate, or nitrosothiols within the blood creating a
local increase in the NO levels at the surface of the material. An
illustrative enzymatic biocatalyst is mammalian xanthine oxidase.
In another illustrative embodiment, a biomimetic catalyst is a
copper (Cu(II)-ligand complex, e.g.
dibenzo[e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclododeca-1,3,7-
,9-tetraene. In some cases, lipophilic salts of nitrite/nitrate
(e.g., tridodecylmethylammonium nitrite (TDMA.sup.+
NO.sub.2.sup.-/NO.sub.3.sup.-)) or certain salts of nitrosothiols
can be doped within a polymer material, or an underlying polymeric
film, to create a reservoir of nitrite or nitrosothiol that
continuously leaks into the immobilized catalytic layer. Adequate
levels of endogenous reducing equivalents are present within blood
to provide catalytically-generated surface levels of NO that are
above the threshold reportedly required to prevent platelet
adhesion or activation.
Inventors: |
Batchelor; Melissa M. (Ann
Arbor, MI), Oh; Bong Kyun (Ann Arbor, MI), Meyerhoff;
Mark E. (Ann Arbor, MI) |
Assignee: |
The Regents of The University of
Michigan (Ann Arbor, MI)
Accord Biomaterials, Inc. (Ann Arbor, MI)
|
Family
ID: |
34959218 |
Appl.
No.: |
11/523,328 |
Filed: |
September 19, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070014829 A1 |
Jan 18, 2007 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10052239 |
Jan 16, 2002 |
7128904 |
|
|
|
60262014 |
Jan 16, 2001 |
|
|
|
|
Current U.S.
Class: |
424/630; 424/423;
435/176; 435/189; 424/426; 435/174; 424/94.4; 435/180; 424/646;
424/600; 435/177 |
Current CPC
Class: |
A61K
33/34 (20130101); A61L 31/16 (20130101); G01N
33/84 (20130101); A61M 1/3672 (20130101); A61M
1/3673 (20140204); C12Q 1/005 (20130101); C12N
11/02 (20130101); C12N 11/14 (20130101); B01J
23/72 (20130101); B01J 31/003 (20130101); B01J
31/1805 (20130101); A61L 2300/114 (20130101); A61M
2202/0275 (20130101) |
Current International
Class: |
A61K
33/34 (20060101); C12N 11/08 (20060101); A61K
38/44 (20060101); A61K 33/00 (20060101); A61K
33/26 (20060101); A61F 2/00 (20060101); C12N
11/00 (20060101); C12N 11/02 (20060101); C12N
9/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
WO 95/04078 |
|
Feb 1995 |
|
WO |
|
WO 99/09912 |
|
Mar 1999 |
|
WO |
|
WO 00/02501 |
|
Jan 2000 |
|
WO |
|
WO 00/11965 |
|
Mar 2000 |
|
WO |
|
WO 00/12112 |
|
Mar 2000 |
|
WO |
|
WO 00/27887 |
|
May 2000 |
|
WO |
|
WO 02/056904 |
|
Jul 2002 |
|
WO |
|
WO 2005/011575 |
|
Feb 2005 |
|
WO |
|
Other References
International Search Report for S.N. PCT/US2006/046013 dated Feb.
20, 2008 (8 pages). cited by other .
International Search Report for S.N. PCT/US2004/034613 dated May
18, 2005 (18 pages). cited by other .
European Search Report for S.N. EP 02 70 75 32 dated Mar. 15, 2005
(5 pages). cited by other .
Supplemental European Search Report for S.N. EP 02 70 75 32.4 dated
Jun. 23, 2005 (8 pages). cited by other .
Annich, G.M. et al., "Reduced platelet activation and thrombosis in
extracorporeal circuits coated with nitric oxide release polymers,"
Crit. Care. Med. 2000 v. 28 915-920 (6 pages). cited by other .
Batchelor, M.M. et al., "More Lipophilic Dialkyldiamine-Based
Diazeniumdiolates: Synthesis, Characterization, and Application in
Preparing Thromboresistant Nitric Oxide Release Polymeric
Coatings," J Med Chem (2003), 46: pp. 5153-5161. cited by other
.
Batchelor M.M. et al., "Preparation and characterization of nitric
oxide releasing polyurethanes for implantable sensor applications,"
Sixth World Biomaterials Congress, Kanuela, HI, May 17, 2000,
Abstract only (1 page). cited by other .
Batchelor, M.M. et al., "More biocompatible polyurethanes via
nitric oxide release," Abstracts of Papers of the American Chemical
Society 222: 405-POLY Part 2, Aug. 2001, Abstract only, (2 pages).
cited by other .
Batchelor, M.M. et al., "More biocompatible polymers via nitric
oxide release," University of Washington Engineered Biomaterials
Conference, Seattle, WA, Aug. 19, 2001 (1 page). cited by other
.
Batchelor, M.M. et al., "Synthesis of nitric oxide-releasing
polyurethane," Proc Am Chem Soc Div PMSE 2001; 84: 594, Abstract
only (2 pages). cited by other .
Batchelor, M.M. et al., "Analytical characterization of novel
nitric oxide releasing polymeric films contiaining
diazeniumdiolates," Pittsburg Conference New Orleans, LA, Abstract
1217, Mar. 16, 2000, Abstract only (1 page). cited by other .
Cha, W. et al., "Direct Detection of S-Nitrosothiols Using Planar
Amperometric Nitric Oxide Sensor Modified with Polymeric Films
Containing Catalytic Copper Species," Anal Chem (2005), 77: pp.
3516-3524. cited by other .
Cha, W. et al., "S-Nitrosothiol Detection via Ampometric Nitric
Oxide Sensor Modified with Polymer film Containing Catalytic
Lipophilic Cu(II)-Complex," The Pittsburgh Conference on Analytical
Chemistry and Applied Spectroscopy, Orlando, FL (2005), Abstract
only, (2 pages). cited by other .
Chandra, S. et al., "Synthesis and spectral studies on copper (II)
complexes of two twelve-membered and tetradentate macrocyclic
ligands," Indian Journal of Chemistry, (Dec. 1998), 37A: pp.
1074-1078. cited by other .
Doel, J. J. et al., "Reduction of Organic Nitrates to Nitric Oxide
Catalyzed by Xanthine Oxidase: Possible Role in Metabolism of
Nitrovasodilators," Biochemical and Biophysical Research
Communications., vol. 270, No. 3, pp. 880-885 (Apr. 2000). cited by
other .
Espadas-Torre, C. et al., "Thromboresistant Chemical Sensors Using
Combined Nitric Oxide Release/Ion Sensing Polymeric Films," J Am
Chem Soc (1997), 119: pp. 2321-2322. cited by other .
Fleser, P.S, et al., "Nitric oxide-releasing biopolymers inhibit
thrombus formation in a sheep model of arteriovenous bridge
grafts," J Vasc Surg 2004, 40: pp. 803-811. cited by other .
Frost, M.C. et al., "In Vivo biocompatibility and analytical
performance of intravascular Clarke-style amperometric oxygen
sensors fabricated with NO-releasing polymers," Pittsburgh
Conference on Analytical Chemistry and Applied Spectroscopy,
Orlando, FL, Mar. 13, 2003, Abstract only (1 page). cited by other
.
Frost, M.C. et al., "Improved in vivo biocompatibility and
analytical performance of implanted electrochemical oxygen sensors
via nitric oxide release," NAMS, Lexington, KY, May 16, 2001,
Abstract only (2 pages). cited by other .
Frost, M.C. et al., "Improved in vivo biocompatibility and
analytical performance of implanted electrochemical oxygen sensors
via nitric oxide release," European Society for Biomaterials
Meeting, London, England, Sep. 13, 2001, Abstract only (2 pages).
cited by other .
Frost, M.C. et al., "Improved in vivo biocompatibility and
analytical performance of implanted electrochemical oxygen sensors
via nitric oxide release," Gordon Research Conference on
Bioanalytical Sensors, Ventura, CA Mar. 12, 2002, Abstract only (1
page). cited by other .
Frost, M.C. et al., "Synthesis and characterization of
S-nitrosothiol derivatized fumed silica for use as nitric oxide
releasing polymer fillers," Society for Biomaterials Meeting,
Tampa, FL, Apr. 25, 2002, Abstract only (1 page). cited by other
.
Frost, M.C. et al., Controlled Photoinitiated Release of Nitric
Oxide from Polymer Films Containing
S-Nitroso-N-acetyl-DL-penicillamine Derivatized Fumed Silica
Filler, J Am Chem Soc (2004), 126: pp. 1348-1349. cited by other
.
Frost, M.C. et al., "Improved In Vivo biocompatibility and
Analytical Performance of Implanted Electrochemical Oxygen Sensors
via Nitric Oxide Release," Society for Biomaterials Meeting, Reno,
NV, May 3, 2003, Abstract only (1 page). cited by other .
Frost, M.C. et al., "Gore-tex vascular grafts with silicone rubbers
capable of releasing nitric oxide for sustained times," American
Society for Artificial Internal Organs, Washington, DC, Jun. 21,
2003, Abstract only (1 page). cited by other .
Frost, M.C. et al., "Improved in vivo biocompatibility and
analytical performance of implanted electrochemical oxygen sensors
via nitric oxide release," Society for Biomaterials Meeting, St.
Paul, MN Apr. 27, 2001, Abstract only (1 page). cited by other
.
Frost, M.C. et al., "Synthesis and characterization of
S-nitrosothiol derivatized fumed silica used as nitric oxide
releasing polymer fillers," American Chemical Society National
Meeting, San Diego, CA Apr. 2, 2001, Abstract 345 only (2 pages).
cited by other .
Frost, M.C. et al., "Analytical characterization of S-nitrosothiol
derivatized fumed silica," Pittsburgh Conference on Analytical
Chemistry and Applied Spectroscopy, New Orleans, LA Mar. 8, 2001,
Abstract only (1 page). cited by other .
Frost, M.C. et al., "Fabrication and In Vivo Evaluation of Nitric
Oxide-Releasing Electrochemical Oxygen-Sensing Catheters," Meth
Enzymol (2004), 381: pp. 704-715. cited by other .
Frost, M.C. et al., "Implantable chemical sensors for real-time
clinical monitoring: progress and challenges," Curr Opin Chem Biol
(2002), 6: pp. 633-641. cited by other .
Frost, M.C. et al, Polymers incorporating nitric oxide
releasing/generating substances for improved biocompatibility of
blood-contacting medical devices, Biomaterials (2005), 26: pp.
1685-1693. cited by other .
Frost, M.C. et al., "Preparation and characterization of
implantable sensors with nitric oxide release coatings,"
Microchemical Journal, 74 (2003) 277-288. cited by other .
Frost, M.C. et al., "Synthesis, characterization, and controlled
nitric oxide release from S-nitrosothiol-derivatized fumed silica
polymer filler particles," J Biomed Mater Res A (2005), 72A: pp.
409-419. cited by other .
Frost, M.C. et al., "In Vivo Biocompatibility and Analytical
Performance of Intravascular Amperometric Oxygen Sensors Prepared
with Improved Nitric Oxide Releasing Silicone Rubber Coating," Anal
Chem (2002), 74: pp. 5942-5947. cited by other .
Hwang, S.Y. et al., "Covalently attached Cu(II)-complex hydrogel as
novel hemocompatible materials," Abstracts of Papers of the
American Chemical Society 228: 292-POLY, Part 2 Aug. 22, 2004,
228th National Meeting of the American-Chemical-Society,
Philadelphia, PA, Aug. 22-26, 2004, Abstract only (3 pages). cited
by other .
Hwang, S.Y. et al., "Covalently attached Cu(II)-complex hydrogel as
novel hemocompatible materials," Abstracts of Papers of the
American Chemical Society 228: 292-Poly, Part 2 Aug. 22, 2004,
228th National Meeting of the American-Chemical-Society,
Philadelphia, PA, Aug. 22-26, 2004, Amer Chem Soc. cited by other
.
Lee, Y. et al., "Improved Planar Amperometric Nitric Oxide Sensor
Based on Platinized Platinum Anode. 1. Experimental Results and
Theory When Applied for Monitoring NO Release from
Diazeniumdiolate-Doped Polymer Films." Anal Chem (2004); 76: pp.
536-544. cited by other .
Lee, Y. et al., "Improved Planar Amperometric Nitric Oxide Sensor
Based on Platinized Platinum Anode. 2. Direct Real-Time Measurement
of NO Generated from Porcine Kidney Slices in the Presence of
L-Arginine, L-Arginine Polymers, and Protamine," Anal Chem (2004),
76: pp. 545-551. cited by other .
Meyerhoff, M.E., "Use of Nitric oxide Releasing/Generating
Polymeric Coatings to Enhance the Biocompatibility of Implanted
Chemical Sensors," 229.sup.th American Chemical Society Meeting,
San Diego, CA, Mar. 2005, Analytical 340, Abstract only (1 page).
cited by other .
Meyerhoff, M.E. et al., "Intravascular Chemical Sensors: Can in
Situ Nitric Oxide Release Solve Lingering Blood
compatibility/Analytical Performance Problems?" The Pittsburgh
Conference on Analytical Chemistry and Applied Spectroscopy, New
Orleans, LA, Abstract 1188, (2000), Abstract only (1 page). cited
by other .
Meyerhoff, M.E., "Improving the bioanalytical chemistry of in vivo
chemical sensors using controlled nitric oxide release," Abstracts
of Papers of the American Chemical Society 228: 132-ANYL, Part 1
Aug. 22, 2004, 228th National Meeting of the
American-Chemical-Society, Philadelphia, PA, Aug. 22-26, 2004, (1
page). cited by other .
Meyerhoff, M.E. et al., Enhancing the biocompatibility and in vivo
performance of intravascular chemical sensors using nitric oxide
release polymers. Abstracts of Papers of the American Chemical
Society 218: U165-U165 132-ANYL Part 1, Aug. 22, 1999, Abstracts
only (2 page). cited by other .
Mowery, K.A. et al., "More Biocompatible Electrochemical Sensors
Using Nitric Oxide Release Polymers," Electroanalysis (1999), 11:
pp. 681-686. cited by other .
Mowery, K.A. et al., "Preparation and characterization of
hydrophobic polymeric films that are thromboresistant via nitric
oxide release," Biomaterials (2000), 21: pp. 9-21. cited by other
.
Mowery, K.A, et al., "The transport of nitric oxide through various
polymeric matrices," Polymer Commun(1999), 40: pp. 6203-6207. cited
by other .
Mowery, K.A. et al., "Thromboresistant Ion-Selective Electrodes Via
Nitric Oxide Release Polymeric Membranes," The Pittsburgh
Conference on Analytical Chemistry and Applied Spectroscopy, New
Orleans, LA (1998), Abstract only (1 page). cited by other .
Mowery, K.A. et al., "Polymeric diazeniumdiolates for fabricating
thromboresistant electrochemical sensors via nitric oxide release,"
Abstracts of Papers of the American Chemical Society 216: U821-U821
034-PMSE Part 2, Aug. 23, 1998, Abstract only (2 pages). cited by
other .
Mowery, K.A. et al., "More biocompatible electrochemical sensors
through the use of combined nitric oxide release ion sensing
polymeric films," Abstracts of Papers of the American Chemical
Society 213: 339-PMSE Part 2, Apr. 13, 1997, Abstract only (2
pages). cited by other .
Mowery, K.A. et al., "More Biocompatible electrochemical sensors
using nitric oxide release polymers," International Symposium on
Electrochemical and Biosensors, Matrafured, Hungary 1998 (2 pages).
cited by other .
Negele, J.C. et al., "Nitric-oxide releasing indwelling oxygen
sensors: Thromboresistivity and performance in dogs," Anesthesia
and Analgesia 90 (2): U90-U90 S134 Suppl. S, Feb. 2000, Abstract
only (1 page). cited by other .
Oh, B.K. et al., "Spontaneous Catalytic Generation of Nitric Oxide
from S-Nitrosothiols at the Surface of Polymeric Films Doped with
Lipophilic Copper(II) Complex," J Am Chem Soc (2003), 25: pp.
9552-9553. cited by other .
Oh, B.K. et al., "Direct Electrochemical Measurement of Nitric
Oxide Release Profile from Diazeniumdiolate Doped Polymer Films,"
Presentation 340, Pittsburg Conference New Orleans, LA, 2000,
Abstract only (1 page). cited by other .
Oh, B.K. et al., "Study of Ion Mediated Reduction of Nitrite to
Nitric Oxide (NO) by Ascorbate," Presentation 646, Pittsburg
Conference New Orleans, LA, 2001, Abstract only (1 page). cited by
other .
Oh, B.K. et al., "Copper-Complex Mediated Nitrite Reduction to
Nitric Oxide (NO) at the Polymer/Solution Interface by
L-Ascorbate," Society for Biomaterials Meeting--28.sup.th Annual,
Tampa, FL, Apr. 25, 2005, Abstract only (1 page). cited by other
.
Oh, B.K. et al., "Catalytic generation of nitric oxide from nitrite
at the interface of polymeric films doped with lipophilic Cu(II)
complex: a potential route to the preparation of thromboresistant
coatings," Biomaterials (2004), 25: pp. 283-293. cited by other
.
Oh, B. K. et al., Biomimetic nitric oxide (NO) generation at
interface of polymeric materials doped with lipophilic
copper(II)-complex,: Dissertation Abstracts International, vol. 64,
No. 9B, p. 4325 (one page) (2003). cited by other .
Parzuchowski, P.G. et al., "Synthesis and Characterization of
Polymethacrylate-Based Nitric Oxide Donors," Am Chem Soc (2002),
124: pp. 12182-12191. cited by other .
Parzuchowski, P.G. et al., "Synthesis of potentially more blood
compatible nitric oxide releasing acrylic copolymers," Abstracts of
Papers of the American Chemical Society 221: U298-U298 27-POLY Part
2, Apr. 1, 2001, Abstract only (2 pages). cited by other .
Reynolds, M.M. et al., "Nitric Oxide Releasing Hydrophobic
Polymers: Preparation, Characterization, and Potential Biomedical
Applications," Free Rad Biol Med (2004), 37: pp. 926-936. cited by
other .
Reynolds, M.M., "Biomimetic Surfaces for Vascular Devices,"
8.sup.th UWEB Summer Symposium, Poster Presentation, Seattle, WA,
Aug. 25, 2004, Abstract only (1 page). cited by other .
Roy-Chaudhury, P. et al., "Local nitric oxide delivery systems:
Implications for transplant preservation," American Journal of
Transplantation 4: 842, Suppl. 8 2004, American Transplant
Congress, Boston, MA, May 14-19, 2004, Amer Soc Transplant Surg;
Amer Soc Transplant, Abstract only (1 page). cited by other .
Roy-Chaudhury P. et al., "Local nitric oxide delivery systems for
dialysis access grafts," Journal of the American Society of
Nephrology 14: 508A-508A, Suppl. S Nov. 2003, 36th Annual Meeting
of the American-Society-of-Nephrology, San Diego, California, Nov.
12-17, 2003, Amer Soc Nephrol SA-PO950, Abstract only (1 page).
cited by other .
Saavedra, J.E. et al., "Conversion of a Polysaccharide to Nitric
Oxide-Releasing Form. Dual-Mechanism Anticoagulant Activity of
Diazeniumdiolated Heparin," Bioorg Med Chem Letters (2000), 10: pp.
751-753. cited by other .
Schoenfisch et al., "Improving the Thromboresistivity of Chemical
Sensors via Nitric Oxide Release: Fabrication and in Vivo
Evaluation of NO-Releasing Oxygen-Sensing Catheters," Anal. Chem.
(2000) 72: pp. 1119-1126. cited by other .
Schoenfisch, M.H. et al., "Nitric Oxide Releasing
Fluorescence-Based Oxygen Sensing Polymeric Films," Anal Chem
(2002), 74: pp. 5937-5941. cited by other .
Schoenfisch, M.H. et al., "Improving the biocompatibility of
intravascular amperometric oxygen sensors via nitric oxide
release," Abstracts of Papers of the American Chemical Society 216:
U158-U158 062-ANYL Part 1, Aug. 23, 1998, Abstract only (2 pages).
cited by other .
Schoenfisch, M.H. et al. "Thromboresistant Fluorescent Optical
Sensors via Nitric Oxide Release," The Pittsburgh Conference on
Analytical Chemistry and Applied Spectroscopy, Abstract 728,
(1999), Abstract only (1 page). cited by other .
Wu, Y., "In Situ Generation of Nitric Oxide (NO) at Polymer/Blood
Interface: Enhancing the Thromboresistivity of Intravascular
chemical Sensors and Other Biomedical Devices," Poster
presentation. 8.sup.th UWEB Summer Symposium, Seattle, WA, Aug. 25,
2004, Abstract only (1 page). cited by other .
Ye, Q. et al., "Surface Morpohology of Thrombsoresistant Nitric
Oxide Release Polymeric Membranes," The Pittsburgh Conference on
Analytical Chemistry and Applied Spectroscopy, New Orleans, LA,
Abstract 334, (2000), Abstract only (1 page). cited by other .
Zhang, H. et al., "Nitric oxide releasing silicone rubbers with
improved blood compatibility: preparation, characterization, and in
vivo evaluations," Biomaterials (2002), 23: pp. 1485-1494. cited by
other .
Zhang, H. et al., "Polymer Films or Coatings Embedded with Nitric
Oxide Releasing Fumed Silica Particles," The 222.sup.nd American
Chemical Society National Meeting, Chicago, IL, United States, Aug.
26-30, 2001, Abstract only (2 pages). cited by other .
Zhang, H. et al., "Novel Silicone Materials with Improved
Thromboresistance via Nitric Oxide Release," The 221.sup.st
American Chemical Society National Meeting, San Diego, CA, United
States, Apr. 1-5, 2001, Abstract only (2 pages). cited by other
.
Zhang, H. et al., "Potentially More Blood Compatible Polymers Using
Nitric Oxide Release Fumed Silica as Fillers," The 220.sup.th
American Chemical Society National Meeting, Washington DC, United
States, Aug. 20-24, 2000, Abstract only (3 pages). cited by other
.
Zhang, H. et al., "More Blood Compatible Silicone Rubbers via
Nitric Oxide Release," The 6.sup.th World Biomaterials Congress,
Hawaii, United States, May 15-20, 2000, Abstract only (2 pages).
cited by other .
Zhang, H. et al., "Synthesis of Nitric Oxide Releasing Silicone
Rubbers for Biomedical Applications," The 218.sup.th American
Chemical Society National Meeting, New Orleans, LA, United States,
Aug. 22-26, 1999, with Abstract (4 pages). cited by other .
Zhang, H. et al., "Nitric Oxide-Releasing Fumed Silica Particles:
Synthesis, Characterization, and Biomedical Application," J Am Chem
Soc (2003), 125: pp. 5015-5024. cited by other .
Zhou, Z. et al., "Combining Nitric Oxide Release with Surface Bound
Heparin: A Potentially More Thromboresistant Polymeric Coating for
Medical Devices," The University of Washington Engineered
Biomaterials 8.sup.th Summer Symposium, University of Washington,
Seattle, WA, USA, Aug. 25-27, 2004, Abstract only (1 page). cited
by other .
Zhou Z.R. et al., "Design, synthesis and characterization of nitric
oxide releasing acrylic copolymers with potentially improved blood
compatibility," Abstracts of Papers of the American Chemical
Society 226: 542-POLY, Part 2 Sep. 2003, 226th National Meeting of
the American-Chemical-Society, New York, New York, Sep. 7-11, 2003,
Amer Chem Soc 19, Abstract only (2 pages). cited by other.
|
Primary Examiner: Naff; David M
Attorney, Agent or Firm: Dierker & Associates, P.C.
Government Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention was made in the course of research partially
supported by a grant from the National Institutes of Health, Grant
Number GM 56991. The U.S. government has certain rights in the
invention.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser.
No. 10/052,239, filed on Jan. 16, 2002 now U.S. Pat. No. 7,128,904,
which claims the benefit of U.S. Provisional Patent Application
Ser. No. 60/262,014 filed on Jan. 16, 2001.
Claims
What is claimed is:
1. An NO releasing material, comprising: a polymer; a neutral
carrier ligand having a planar square geometry; and a metal ion
bound to the neutral carrier ligand; wherein said material
generates nitric oxide when in contact with a nitrate, a nitrite or
a nitrosothiol.
2. The NO releasing material of claim 1 wherein said neutral
carrier ligand is at least one of: a N.sub.x-donor macrocyclic
ligand or a S.sub.x-donor macrocyclic ligand, wherein x is
independently selected from the group consisting of 2, 4, 5, 6 or
8.
3. The NO releasing material of claim 2 wherein said ligand is a
N.sub.x-donor macrocyclic ligand selected from: cyclen, cyclam or
derivatives thereof, or a crown ether.
4. The NO releasing material of claim 1 wherein said metal ion is
selected from Fe(III) or Cu(II).
5. The NO releasing material of claim 1 wherein the polymer is
selected from polyurethane, polydimethylsiloxane, ethylene vinyl
acetate, nylon, polyacrylic, polymethyl methacrylate, polyamide,
polycarbonate, polyester, polyethylene, polypropylene, polystyrene,
polytetrafluoroethylene, cellulose acetate, poly(vinyl chloride),
and silicone rubber.
6. A biocompatible material comprising a metal coated with the NO
releasing material of claim 1.
7. A medical device comprising the NO releasing material of claim
1.
8. An NO releasing material, comprising: a polymer; a neutral
carrier ligand having a planar square geometry; and a metal ion
bound to the neutral carrier ligand; wherein said material
generates nitric oxide when in contact with a nitrate, a nitrite or
a nitrosothiol; and wherein said ligand is selected from
dibenzo[e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-te-
traene;
dibenzo[e,k]-2,3,8,9-tetramethyl-1,4,7,10-tetraaza-cyclododeca-1,3-
,7,9-tetraene;
dibenzo[e,k]-2,3,8,9-tetraethyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-tet-
raene, and/or salts thereof.
Description
BACKGROUND
This invention relates generally to biocompatible materials, such
as polymers or metals, and more particularly, to biocompatible
materials having blood interface surfaces that are capable of
biocatalytic or biomimetic generation of nitric oxide in situ when
contacted with endogenous nitrite, nitrate, or nitrosothiols in
blood.
Although medical devices such as extracorporeal circuits and
hemodialysis tubes are widely used in clinical settings, the
polymers typically used to fabricate such devices (PVC,
polyurethane, silicone rubber, etc.) are still subject to platelet
aggregation and adhesion onto the surface of these materials. Thus,
patients are often given anti-clotting agents (i.e., heparin) in
order to reduce thrombosis on the surface of these devices.
Similarly, implanted devices made of stainless steel or other
alloys, or even carbon, can cause thrombus formation when in direct
contact with blood. There is, therefore, a need for materials that
more closely simulate the antithrombogenic properties of the
endothelial cells that line blood vessels in order to obviate the
need to administer anticoagulants.
Nitric oxide (NO) is an important intracellular and intercellular
messenger molecule that plays an important physiological role in
anti-platelet aggregation and anti-platelet activation, vascular
relaxation, neurotransmission, and immune response. It has been
proposed that synthetic materials that release low levels of NO
would, therefore, more closely simulate the natural activity of
endothelial cells, and therefore, would have improved
biocompatibility.
Several classes of NO-releasing materials are currently under
investigation worldwide. These include NO donors (i.e.,
diazeniumdiolates, nitrosothiols) that may be relatively
complicated to synthesize and may, in some instances, require
stringent storage conditions. Thus, there is a need for improved
materials that are easier to fabricate and store.
Currently, NO generation is determined by water uptake (such as in
the case of diazeniumdiolates) or the intensity of light (as with
iron nitrosyls). However, blood already contains a host of species
that are derived from, or are physiologically-generated in vivo
that can be reduced to NO. These species include nitrites,
nitrates, and a host of nitrosothiols (e.g., nitrosoglutathione,
nitroso albumin, etc.). This raises the possibility of recycling
these species back to nitric oxide. There is, therefore, a need for
materials that can reduce these species to nitric oxide locally at
the substrate/blood interface.
It is an object of this invention to provide improved materials for
biomedical applications that are capable of releasing NO from
blood-contacting surfaces materials, so as to prevent platelet
activation and adhesion onto these surfaces, thereby lowering
thrombus formation and other complications associated with
interactions between blood and foreign materials.
It is a further object of this invention to provide improved
materials for biomedical applications that are relatively
inexpensive to manufacture and that have improved
biocompatibility.
It is still a further object of this invention to provide materials
for biomedical applications that are capable of releasing NO from
blood-contacting surfaces materials in response to nitrites,
nitrates, and nitrosothiols in the blood.
SUMMARY
The foregoing and other objects are achieved by embodiment(s) of
this invention, which provide a novel approach for enhancing the
biocompatibility of materials of the type suitable for implantation
in a human or animal body and/or for prolonged contact with the
body or blood. In accordance with a broad aspect of the invention,
materials have been developed to have a catalytic surface that is
capable of generating, at the catalytic surface/blood interface,
physiologically significant amounts of NO when in contact with
blood. A catalytic agent, having nitrite reductase activity and/or
nitrite reductase-like activity, or nitrosothiol reductase
activity, is immobilized, adsorbed, adhered, or otherwise made
available at a surface of the material.
In some embodiments, the catalytic agents are biocatalysts, such as
enzymes, having nitrite reductase and/or nitrite reductase-like
activity, or nitrosothiol reductase activity. Illustrative examples
of the biocatalyst include nitrite reductases, nitrate reductases,
enzymes having nitrosothiol reducing ability, and xanthine oxidase,
or combinations thereof. Due to the ease of procuring xanthine
oxidase commercially (e.g., Sigma, St. Louis, Mo.), xanthine
oxidase is a preferred embodiment. Other potentially useful
immobilized biocatalysts include nitrite reductases and nitrate
reductases from plants or bacteria.
In other embodiments, the catalytic agent is a biomimetic catalytic
agent. As used herein the term "biomimetic catalytic agent" refers
to a species possessing nitrite reductase-like activity, or the
ability to reduce nitrosothiols which converts endogenous or
exogenous nitrite/nitrate or nitrosothiols to NO when in contact
with blood.
Illustratively, the biomimetic catalytic agent is a metal ion
ligand complex wherein the metal ion is capable of reducing one or
more of nitrite, nitrate, nitrosothiols, and other blood species to
nitric oxide. In particularly preferred embodiments, the metal ion
ligand complex is a Cu(II) complex. Neutral carrier type ligands
that have high metal binding affinity, particularly for copper, are
suitable for use in the practice of the invention. Further suitable
neutral carrier type ligands include those having planar
square-type geometry that provides a minimum amount of steric
hindrance to the approach of the electron source (e.g., ascorbate
or NADH) to the center metal of the complex so that the copper ion
can easily be reduced from Cu(II) to Cu(I). Examples include,
without limitation, nitrogen or sulfur donating compounds, such as
N.sub.x-donor s (x=2, 4, 5, 6, 8) such as cyclen, cyclam and their
derivatives, and crown ethers and S.sub.x-donor macrocyle-type
ligands (x=2, 4, 5, 6, 8).
In specific illustrative embodiments, the biomimetic catalyst is a
Cu(II) metal ion ligand complex selected from the group consisting
of
dibenzo[e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-te-
traene;
dibenzo[e,k]-2,3,8,9-tetramethyl-1,4,7,10-tetraaza-cyclododeca-1,3-
,7,9-tetraene; and
dibenzo[e,k]-2,3,8,9-tetraethyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9,-te-
traene.
As used herein, the term "material," when referring to the material
that is provided with the catalytic surface, may be any material.
In an embodiment, the material is of a type that is suitable for
contact with the body and/or body fluids, particularly blood, of a
living being, e.g., a material that is physiologically acceptable
and non-toxic. In some embodiments, the material should be suitable
for long-term contact, or in-dwelling uses. Non-limitative examples
of such materials include polymers, metals and alloys thereof, and
carbon (graphite).
Many polymeric materials are suitable for the practice of the
invention, and the following illustrative list of polymers that has
been used for biomedical applications, is not intended to be
limiting in any manner. Examples include synthetic polymers such as
polyurethane, polydimethylsiloxane, ethylene vinyl acetate, nylons,
polyacrylic, polymethyl methacrylate, polyamide, polycarbonate,
polyester, polyethylene, polypropylene, polystyrene, poly(vinyl
chloride) (PVC), polytetrafluoroethylene (PTFE), and cellulose
acetate.
In an embodiment, the material includes a hydrophobic polymer
substrate, such as poly(vinyl chloride), polyurethane, and silicone
rubber, and a layer of a catalytic agent having nitrite reductase
activity and/or nitrite reductase-like activity, or nitrosothiol
reductase activity attached to a surface of the hydrophobic polymer
substrate. The attachment may be by adsorption, covalent bonding,
and the like. In an embodiment, the polymer substrate may include
lipophilic salts of nitrite, nitrates, or nitrosothiols within its
matrix to create a reservoir of nitrite, nitrate, or nitrosothiol
that can continuously leak to the catalytic surface.
In embodiments where the "material" is a polymer, the NO-releasing
polymer can be formed, cast, or otherwise shaped to form a
monolithic device, such as an implantable device (e.g. a drug
depot) or in-dwelling devices, (e.g. catheters, or extracorporeal
tubing sets (non-limitative examples include kidney dialysis or
open-heart surgery heart-lung machines)) and/or the like. The
polymer may also be applied as a film on another substrate, such
as, for example, a polymer substrate, or on another surface, such
as, for example, the surface of a metal device.
Suitable metals include, but are not limited to, stainless steel,
nickel, titanium, aluminum, copper, gold, silver, platinum and
combinations thereof. The metal material may form medical devices.
The following types of devices, provided with a catalytic agent in
accordance with the principles of the invention, are meant to be
illustrative, but not limiting, examples: arterial stents, guide
wires, catheters, bone anchors and screws, protective platings, hip
and joint implants, spine appliances, electrical leads, biosensors,
and probes.
Further, the material may be a metal substrate. In an embodiment,
the metal substrate may have a biomimetic catalytic agent
covalently attached to its surface. As stated above, in an
embodiment, the biomimetic catalytic agent is a metal ion ligand
complex which is capable of reducing one or more of nitrite,
nitrate, nitrosothiols, and other blood species to nitric oxide. In
particularly preferred embodiments, the biomimetic catalytic agent
is a Cu(II) metal ion ligand complex. Attachment of the metal ion
ligand to the metal surface may be accomplished by any suitable
means. One such technique involves silanizing the surface of the
metal to provide reactive sites to bind the ligand.
In certain embodiments, an exogenous source of nitrites, nitrates,
or nitrosothiols is provided in the polymer to form a reservoir of
nitrite, nitrate, or nitrosothiol that can continuously leak to the
catalytic surface of the material. In these embodiments, the
exogenous source (a non-limitative example of which includes
lipophilic salts of nitrites, nitrates, or nitrosothiols) is
dispersed within the material. In some embodiments, the polymeric
material containing the exogenous source of nitrite/nitrate or
nitrosothiol is applied to a catalytic surface as a coating. Some
non-limitative examples of the source of nitrites, nitrates, or
nitrosothiols, include, without limitation, quaternary ammonium
salts, such as tridodecylmethylammonium nitrite (TDMA.sup.+
NO.sub.2.sup.-/NO.sub.3.sup.-); trimethyl phenyl ammonium; dimethyl
dioctadecyl ammonium; etc. In addition to quaternary ammonium
salts, quaternary phosphonium salts or quaternary arsonium salts
may be used in the practice of embodiments of the invention.
Methods of making the invention include swelling a polymer, such as
a poly(vinyl chloride) (PVC) or silicone, in the presence of an
organic solvent containing an appropriate nitrite/nitrate salt to
form a nitrite/nitrate salt-containing polymer. The nitrite/nitrate
salt-containing polymer is then coated with a layer of immobilized
enzyme, illustratively a nitrite reductase enzyme, such as xanthine
oxidase. Many techniques are available for immobilizing enzymes.
For example, see, Hasselberger, "Uses of Enzymes and Immobilized
Enzymes, Nellson-Hall," Chicago (1978) or Guilbault, "Analytical
Uses of Immobilized Enzymes," Marcel Dekker, New York (1984).
In another embodiment of the method, the biomimetic generation of
NO may be achieved by immobilizing metal-ion ligand complexes, on
the surface of the material, or by dispersing these ligands within
the material, which may be a polymer. In some embodiments,
additional lipophilic nitrite/nitrate salts, or nitrosothiols, are
added to an underlying polymer matrix material or provided as a
coating on the material, or as an additional layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Comprehension of embodiment(s) of the invention is facilitated by
reading the following detailed description, in conjunction with the
annexed drawing, in which:
FIG. 1 is a schematic illustration of NO generation in solution via
nitrite reductase activity from the catalytic surface of a polymer
loaded with nitrite salt;
FIG. 2 is a graphical representation of the NO-release profile from
nitrite ion-pair doped polymer films having immobilized XO on the
surface in the presence of sheep blood;
FIG. 3 is a schematic representation of NO generation from a
polymer matrix that has been loaded with a nitrate salt and a
Cu(II) ligand complex in accordance with the invention;
FIG. 4 is a schematic representation of a material, in accordance
with the invention, wherein a Cu(II) ligand complex is covalently
tethered to the surface;
FIG. 5 is a graphical representation of the surface generation of
NO from a Cu(II) ligand complex-containing polymer film in a bulk
solution containing nitrite and ascorbate;
FIG. 6 shows three examples of illustrative metal ligand complexes;
and
FIG. 7 is a graphical representation of NO generation from a
nitrite ion pair/Cu(II) complex, specifically the complex
designated L2 in FIG. 6.
DETAILED DESCRIPTION
In one embodiment of the method for making an improved NO-releasing
polymer, the desired polymer may be swelled in an organic solution
containing the lipophilic nitrite/nitrate salt. In other
embodiments, the salt can be added during the processing stage when
the desired end product is molded or cast from the native polymer
material. In still other embodiments, the surface of the polymer
material that will be exposed to blood (non-limitative examples of
which include the outside surface of a catheter, the inner surface
of tubing of the type used in extracorporeal circuits, or the
surface of metal stents) may be coated, either by dip-coating or by
another method, with a biocatalyst (enzyme) or biomimetic catalyst
capable of reducing nitrate, nitrite, or nitrosothiols to NO. The
biocatalysts or biomimetic catalysts can also be covalently
tethered to the surface of the material.
FIG. 1 illustrates a specific embodiment of the material of the
present invention. Mammalian xanthine oxidase (XO) is used as the
surface catalyst for nitrite reduction to NO. In the presence of
nicotinamide adenine dinucleotide (NADH), or other reducing
equivalents in blood, the surface catalyst will generate NO as the
nitrite ions leak from within the material into this surface layer
via exchange for chloride and bicarbonate within the blood.
Referring to FIG. 1, a polymer matrix 11 that has been loaded with
a lipophilic nitrite/nitrate salt of tridodecylmethylammonium 12
(R.sup.+NO.sub.2.sup.-) that provides a source of nitrite ions
(NO.sub.2.sup.-). A coating 13 of xanthine oxidase (XO) is located
at the surface of the polymer matrix 11.
Preliminary feasibility studies have been carried out to
demonstrate the basic concept of this invention. Xanthine oxidase
was used as a model enzyme for nitrite reductase activity. PVC
polymer films were doped with TDMA.sup.+ NO.sub.2.sup.- and then
coated with a layer of immobilized XO.
Illustratively, the PVC polymeric film, or membrane, was prepared
by a cocktail solution casting method as described, for example, in
Mathison et al., Anal. Chem., Vol. 71, pages 4614-4621 (1999) or
any of the patents referenced herein. The cocktail solution was
prepared by dissolving the appropriate amounts of membrane
components (polymer, plasticizers and, in some cases, an
ion-exchanger) into a solvent, illustratively tetrahydrofuran
(THF). The membranes were cast in a mold to a final thickness of
about 150 .mu.m.
The polymer film was then coated with immobilized XO, prepared by
crosslinking XO with bovine serum albumin (BSA) in the presence of
glutaraldehyde. The cross-linked product forms a hydrogel that is
dip-coated on the PVC polymer substrate.
An electrochemical sensor was used to probe the surface
concentrations of NO generated when the coated film was placed into
a buffered solution containing NADH at physiological pH.
Significant levels of NO were generated at the surface of the film
under these conditions. The generation of NO near the surface of
the polymer film continued for several hours as the nitrite in the
film was exchanged for anions in the buffer phase.
In this particular embodiment, the electrochemical NO sensor used
was similar in style to a conventional Clark type oxygen sensor. A
glass coated Platinum (Pt) wire served as the anode and a Ag/AgCl
wire (0.25 mm dia.) was used as the cathode. The internal filling
solution was composed of 0.3 mM HCl and 30 mM NaCl, pH 3.5. An
outer gas permeable membrane (Goretex, polytetrafluoroethylene with
50% porosity and 0.2. .mu.m pore size) was placed between the
internal filling solution and sample solution. Amperometric NO
measurements were performed using an electrochemical analyzer.
FIG. 2 graphically illustrates that, when a similar film coated
with XO was exposed to whole sheep blood, without the addition of
any reducing equivalents in the form of NADH, measurable levels of
NO were generated at the surface of the film as detected by the
aforementioned electrochemical NO sensor. This data suggests that
there is adequate endogenous reducing equivalent species in blood
to serve as the source of electrons for the biocatalytic reaction
at the surface of a polymer prepared in accordance with the present
invention.
In another illustrative embodiment, biomimetic catalysts, such as
Cu(II)-ligand complexes, for example,
dibenzo[e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-te-
traene, were either incorporated in or tethered to a polymer or
other material surface, such as a metal. Examples of this
embodiment are shown in FIGS. 3 and 4.
FIG. 3 is a schematic representation of a polymer matrix 31,
illustratively PVC, that has been loaded with a lipophilic Cu(II)
ligand complex 32 as well as a lipophilic nitrite/nitrate salt of
tridodecylmethylammonium 33 (N.sup.+NO.sub.2.sup.-) that provides a
source of nitrite ions (NO.sub.2.sup.-) in the polymer. When the
polymer 31 is exposed to an aqueous solution containing ascorbate
(ASC) or ascorbic acid, the ascorbic acid reduces the Cu(II) in the
ligand complex 32 to Cu(I). The Cu(I) in turn reduces nitrites in
the film to NO.
FIG. 4 is a schematic representation of a material 40 that has a
catalytic surface 41 created by tethering a Cu(II) ligand complex
42 to the surface. When the catalytic surface 41 is exposed to an
aqueous solution, which may be blood, containing ascorbic acid, the
ascorbic acid reduces Cu(II) in the ligand 42 to Cu(I). The Cu(I)
returns to Cu(II), thereby converting nitrites and nitrosothiol
(RSNO), for example, in the solution to NO.
FIG. 5 is a graphical representation of the surface generation of
NO from a Cu(II) ligand complex-containing polymer film in a bulk
solution containing nitrite and ascorbate. The data is plotted as
NO concentration in parts per billion (ppb) as a function of time
in seconds.
Three films having the following formulation were prepared in
accordance with the method set forth above: 66.7 wt % PVC polymer
(132 mg); 33.3 wt % plasticizer, illustratively nitrophenyloctyl
ether (NPOE; 66 mg), and Cu(II) ligand complex, CuL.sub.xC1.sub.2
(2 mg), L.sub.x being one or more of ligands L1-L3 as shown on FIG.
6. The illustrative metal ligand complexes, specifically Cu(II)
ligand complexes, shown in FIG. 6 are
dibenzo[e,k]-2,3,8,9-tetramethyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-te-
traene, labeled L1;
dibenzo[e,k]-2,3,8,9,-tetraethyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-te-
traene, labeled L2; and
dibenzo[e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclodeca-1,3,7,9-tetr-
aene, labeled L3.
Although these complexes are shown as chloride salts, it is to be
understood that other counterions are appropriate. Other metal ions
were evaluated for activity, i.e., ability to mediate the reduction
of nitrite to NO by ascorbate, including Co(II), Ni(II), Zn(II)
Mn(II), Al(II), and Fe(III). Of these ions, Fe(III) yielded a
detectable level of NO, but this was far less than that observed
with Cu(II) under identical conditions. Other metals, such as
V(III), Cr(III), and Ti(III) have also been suggested as being
capable of reducing nitrite to NO. However, unlike Cu(II) or
Fe(III), these metals are not present in appreciable levels in
vivo, either within physiological fluids or within specialized
cellular vesicles. Therefore, Cu(II) is presently the preferred
metal ion for the practice of the invention.
Referring back to FIG. 5, the traces represent ligands L1-L3,
respectively. In this particular experiment, the bulk solution was
deoxygenated phosphate buffered saline (PBS) having a pH of 7.4. At
time t=0, 1 mM nitrite and 1 nM ascorbate were added to the PBS
solution and NO generation was measured with a chemiluminescense
detector. The results demonstrate that films in accordance with the
present invention are capable of NO generation at the interface
when the nitrites and ascorbates are in the bulk solution, such as
would occur when the films were placed in contact with blood in an
in vivo situation.
FIG. 7 is a graphical representation of NO generation from a
nitrite ion pair/Cu(II) complex, specifically the complex
designated L2 in FIG. 6, doped into a polymer film. The data is
plotted as NO concentration in parts per billion (ppb) as a
function of time in minutes following the introduction of 1 mM
ascorbate into a deoxygenated PBS solution having pH 7.4.
The polymeric film compositions used in this experiment are as
follows:
Film 1:
66 mg PVC; 132 mg NPOE; 4 mg Cu(II) complex; and 20 mg ion pair or
TDMA.sup.+NO.sub.2.sup.-
Film 2:
100 mg PVC; 100 mg NPOE; 4 mg Cu(II) complex; and 20 mg ion
pair
Film 3:
132 mg PVC; 66 mg NPOE; 4 mg Cu(II) complex; and 20 mg ion pair
These results show generation of NO by the polymer film that is
particularly good for the highly plasticized embodiments.
The major advantage of this technology over the previous methods
for generating NO locally at the surface of polymers or other
materials is the potential simplicity of simply dip-coating the
material with a biocatalytic or biomimetic catalytic layer. The
catalytic layer may have a single catalyst or a mixture of
reductase activities. It may be a biological protein (enzyme) or a
metal ion-ligand complex that mimics the enzyme function. Even in
those embodiments where added TDMA.sup.+
NO.sub.2.sup.-/NO.sub.3.sup.- or some other nitrite/nitrate salt,
or a nitrosothiol, such as nitroso cysteine, is required or
desired, within the material, the stability of such species is
likely to far exceed the stability of diazeniumdiolates and other
NO donors used to date.
In a clinical situation, it should be noted that, even if the
amount of reducing equivalent species in the blood were to vary
from test subject to test subject, it is possible to add reducing
equivalents of an alternate electron donor to the blood,
illustratively in the form of ascorbic acid, by administering low
doses of Vitamin C to the patient. This may aid in ensuring the
presence of adequate levels of reducing equivalents.
Although the invention has been described in terms of specific
embodiments and applications, persons skilled in the art can, in
light of this teaching, generate additional embodiments without
exceeding the scope or departing from the spirit of the invention
described herein. Accordingly, it is to be understood that the
drawing and description in this disclosure are proffered to
facilitate comprehension of the invention, and should not be
construed to limit the scope thereof.
* * * * *